3.2. Process Prerequisite Section

Next, the Prerequisite Section is checked to see that all prerequisites are satisfied by the current state of the zone. Using the definitions expressed in Section 1.2, if any RR's NAME is not within the zone specified in the Zone Section, signal NOTZONE to the requestor.

3.2.1. For RRs in this section whose CLASS is ANY, test to see that TTL and RDLENGTH are both zero (0), else signal FORMERR to the requestor. If TYPE is ANY, test to see that there is at least one RR in the zone whose NAME is the same as that of the Prerequisite RR, else signal NXDOMAIN to the requestor. If TYPE is not ANY, test to see that there is at least one RR in the zone whose NAME and TYPE are the same as that of the Prerequisite RR, else signal NXRRSET to the requestor.

3.2.2. For RRs in this section whose CLASS is NONE, test to see that the TTL and RDLENGTH are both zero (0), else signal FORMERR to the requestor. If the TYPE is ANY, test to see that there are no RRs in the zone whose NAME is the same as that of the Prerequisite RR, else signal YXDOMAIN to the requestor. If the TYPE is not ANY, test to see that there are no RRs in the zone whose NAME and TYPE are the same as that of the Prerequisite RR, else signal YXRRSET to the requestor.

3.2.3. For RRs in this section whose CLASS is the same as the ZCLASS, test to see that the TTL is zero (0), else signal FORMERR to the requestor. Then, build an RRset for each unique <NAME,TYPE> and compare each resulting RRset for set equality (same members, no more, no less) with RRsets in the zone. If any Prerequisite RRset is not entirely and exactly matched by a zone RRset, signal NXRRSET to the requestor. If any RR in this section has a CLASS other than ZCLASS or NONE or ANY, signal FORMERR to the requestor.

3.2.4. Table Of Metavalues Used In Prerequisite Section

   CLASS    TYPE     RDATA    Meaning
   ------------------------------------------------------------
   ANY      ANY      empty    Name is in use
   ANY      rrset    empty    RRset exists (value independent)
   NONE     ANY      empty    Name is not in use
   NONE     rrset    empty    RRset does not exist
   zone     rrset    rr       RRset exists (value dependent)

3.2.5. Pseudocode for Prerequisite Section Processing

      for rr in prerequisites
           if (rr.ttl != 0)
                return (FORMERR)
           if (zone_of(rr.name) != ZNAME)
                return (NOTZONE);
           if (rr.class == ANY)
                if (rr.rdlength != 0)
                     return (FORMERR)
                if (rr.type == ANY)
                     if (!zone_name<rr.name>)
                          return (NXDOMAIN)
                else
                     if (!zone_rrset<rr.name, rr.type>)
                          return (NXRRSET)
           if (rr.class == NONE)
                if (rr.rdlength != 0)
                     return (FORMERR)
                if (rr.type == ANY)
                     if (zone_name<rr.name>)
                          return (YXDOMAIN)
                else
                     if (zone_rrset<rr.name, rr.type>)
                          return (YXRRSET)
           if (rr.class == zclass)
                temp<rr.name, rr.type> += rr
           else
                return (FORMERR)

      for rrset in temp
           if (zone_rrset<rrset.name, rrset.type> != rrset)
                return (NXRRSET)